Yes, you don't always have time to sit down to a full test. Any practice is beneficial.

There are twp aspects for preparations:
1. Learning
2. Checking the preparations

Learning should consume 95% of your efforts and checking just 5%.

From learning perspective, the effectiveness is always high when you study in smaller chunks i.e. take questions in smaller sets like 40/50/100. By taking questions in smaller chunks, you do not get tired and you have ample time to validate your weak areas (gaps).

You should also try your preparation check, here you can take 2-3 simulation test of 200 questions. I would say, 2-3 is sufficient enough as you do not learn and you cannot effectively utilize this mode of practice.

In short, you preparation should be combination of both techniques, but more emphasis should always be on effective mode of learning.

Saket, PMP