Can I use 8pF 200ohm 10MHz crystal with ATMega88 w/o caps?
This ESE answer contains a good explanation of what having an incorrect load capacitance could do.

Personally I would never do this, because I don't like coming back to pain-in-the-butt problems when they surface much later down the line - I like to ensure they never happen instead.

From this TI Application report we can estimate around 1-3pF of stray capacitance per inch of trace for a PCB with a power and ground plane, Bear in mind that given the high contribution from fringing fields (as the capacitor's gap is larger than its width) you will get material permittivity contributions from your solder resist as well as the FR4 of the PCB. Hence if you are relying on a few stray pF to get you through, a different resist process might have a relatively large impact on this. As you note in your question, this is why crystals with a higher loading requirement are easier to design with - a larger percentage of the load capacitance is in the tightly-controlled precision component you paid for, and less in the vagaries of the PCB production process.

If space is an issue for you, have you considered either using an internal oscillator source or a ceramic resonator (which is a one-component solution) as an alternative? Neither will have the same accuracy or stability as a crystal, but you may find you don't actually need that timing accuracy in your application.