Pressure cooking beans with salt and spices
The main impact I find is on flavor. If you're in a hurry and just want a one-pot recipe, go for it, throw it all in and let it cook. Most Indian spices are fairly robust and should withstand the pressure-cooking process. But you may get better results if you cook some of separately, especially if you're already going to be cooking onions, garlic and ginger to add in. I do often include some salt during cooking because I feel that it helps to flavor the food better, similar to the way I was taught to cook pasta (salt the water the pasta cooks in and give a lighter hand to the salt in the sauce).

You really can still generally get reasonably good results without worrying too much about this stuff. It's just that you may get better results if you pay closer attention to when you add what. :-) But if the main result that you want is no-hassle, quick cooking, then who am I to tell you what you really want from your food?

You will certainly get a slightly different flavor from spices depending on how you handle them. Some herbs become bitter if they're cooked a long time (oregano), others lose their flavor pretty much entirely if you cook them longer (dill, mint). Others develop a more complex flavor profile if they are roasted first (cumin, coriander seed). 

If I am cooking with cloves, cinnamon, bay leaves, cardamom -- really aromatic things that I usually remove after cooking -- I usually include these during the pressure-cooking and remove them when I open the cooker. They will have imparted a strong flavor and aroma into the beans and the cooking water and I don't need more from them. My mom always removes bay leaves before she packs away any left-overs because she finds that they continue to impart an ever stronger flavor into the food while in the fridge. I find the same is true of cinnamon sticks. (Cloves and cardamom not quite as much, I just don't like to bite into them as I'm eating the food.)

I usually cook the other spices separately in another pan with whatever onion/ginger/garlic/etc while the beans are cooking, then add those all together to the beans after the beans have finished cooking.

If you're starting from a pre-blended spice mix, I would probably treat that like the latter and cook it with the onions, etc, and add it towards the end. That doesn't mean you can't throw all of it (onions and all!) into the pressure cooker and have it cook together, but an onion that goes into the beans and water raw will impart a different flavor from that of a caramelized onion. The same goes for raw vs cooked tomato and various other ingredients in Indian cooking. 

There are some recipes where I like the effect of just throwing everything in together raw (usually soups, stews, chili, baked beans) but for others I find that taking the extra effort of handling some things differently pays off. (I also find that starting from fresh spices IF you use them frequently makes a big difference vs pre-mixed spice blends, but then again, sometimes having the pre-mixed blends to fall back on can be a nice change, too.)

From a health perspective, cooking vegetables and spices in the pressure cooker will raise the cooking temperature vs boiling. Any nutrients that are adversely affected by high heat may be further affected by pressure cooking vs cooking on an open pan on the stove. Most herbs and spices are of fairly negligible nutritional value to begin with (at least, in the quantities we cook with) so I wouldn't worry about this type of nutrient loss from spices.

Water-soluble nutrients from the beans or from greens like spinach and kale are still present in the cooking liqueur, so as long as you don't discard that after cooking, you aren't losing a lot of nutrients there, either. 

From a time perspective, I have never noticed any difference in the time it takes to cook lentils if I have the onions, tomatoes and spices in with them, but I also haven't tried to shave the time down to the minimum there, either. 

If you're in a really big hurry or if you have some older beans that are being stubborn about rehydrating, you can add a little bit of baking soda to the cooking water to help them to soften up.  Use very little (&lt;1/2 tsp in a big pot) or plan to discard the cooking water. If you are using baking soda you can change the water half-way through and add the spices at that point for a compromise.

This is based on how I learned to cook American food from my mom and that side of the family and Indian food from my in-laws and college roommates, etc, as well as a lot of experimentation. :-)