They could be implemented in areas where it makes sense, ambushes in thick jungle, dark caves etc. Makes no sense at all to be surprised on a huge plain without so much as a shrub to hide behind or in the middle of a busy city street (monsters, that is).
Of course, I'm a long time pen & paper RPG fan so I'm a little particular about my feelings in this, encounters should always make sense imo and in many JRPG's (and WRPG's) they just don't.







