1. If the family is simple rectangular which can be created using default family templates ( Door, Window, repeat details, wall based plumbing fixtures etc ) or can be created using few changes to existing ( default ) families, then one should create them as simple families.
2. Advantage for those families are you can give custom parameters specially like Materials, Offset from levels,
height, width etc..
3. Another advantage is you can save those families ( right click on family in project browser and save all in one folder for further use )
4. In place families are great only if they are one off.. you cannot use them in different project cause revit doesnt allow copy and paste it into new projects..
5. inplace families are little hard to schedule.. ( like extracting their diemnsion parameters , also applying material is requires editing them all the time , and if you have multiple instances of inplace families, its hard to apply same material to all of them in one go for example... )
so its a users call usually whether to create in-place families.. but generally, if you are investing time in creating them anyways, why not use default templates for families and create them...
trick is also you can have nested families... ex.. create a wash basin which is not wall based..but then you can insert that was basin family into another wall based family... and then load in the project..
best luck..
Corsten
Building Designer