When I was a kid, I would play one or two different strategies in the games we played and that was about it. I watch the people at game night and I would say half the crowd like to play the same strategies from one game to another.
When you are a playtester, you should take the opportunity to try as many different strategies as you can. Not only will you expand your gaming horizons, but you will help out the game and the designer when it comes to making updates.
Trying different strategies is all about stressing the game and seeing how it reacts. Stressing the game will put the game in places it has never been before. This really helps the designer get familiar with the random situations their game can get into that they never thought of.
Not only does the game benefit, but the game can be a more interesting and fun exploration of the game for you, the playtester.
If you have any comments or questions, leave a comment here or email Chris at firstname.lastname@example.org