Hey there.
It is not bad to have 3, or even 5 sided polys in your mesh, this is a myth. The only time when having non-quad faces in your mesh may present a problem is if you want to convert your mesh to a sub-d surface, or if your mesh has 3 or n-sided faces where you need a mesh to deform for animation, for example. It is possible to always model using only 4-sided faces, but sometimes this can be impractical, as you may need to add lots of extra polys and edge loops to get rid of all the 3 or 5 sides.