Advantages of Four pin mosfet
There's no general "A is better than B", in engineering, ever.

Your senior pointed you to a four-pin MOSFET for a specific reason – that might the ability to carry away more heat from the package, higher current rating, better mechanical mounting, easier solderability, a large stock of exactly these in the basement that's basically free … ask them!

It's relevant which part of the MOSFET the fourth pin actually contacts: All MOSFETS (far as I can see) will have drain, source, gate contacts, but what about Bulk?

The one you linked to has a "split" source pin, and that allows you to connect a high-current trace to that and a measurement / voltage reference trace to the other. Again, that's an engineering reason. That's not "better" than a different MOSFET (it's larger, at the very least, so that's actually a problem), it solves a specific problem that your design has.

Everything has context: If you are an engineer, always know why you're doing something. Becoming senior means exactly that: having had enough experience to know why you should be doing something, and not something else. You can learn "always use a four-pin MOSFET in XYZ situation" from a book, but that's not seniority. Seniority is having an idea of what goes wrong when you don't. Because that allows you to actually do trade-offs.

So, if that person deserves that name, she or he should be able to explain to you why you should be doing that, of course if their time permits and after you've done your own research. In my experience, engineers with a high level of expertise will want to share that with you, because it means they have one more person that knows their stuff (and doesn't do mistakes that they'll have to fix later on, keeping them from things they find interesting). So, by all friendly, honest means: Ask them!