Please help me understand this SSHE concept

[pstripling]

I have been reviewing SSHE alot lately and wanted some clarification on this preflop concept. The middle pair hands (77-99) are giving me just a bit of trouble from EP and early MP.

If the table is an average 3/6 10 handed game on PartyPoker with the usual mix of suspects what is the default play with these hands when it is folded to you OR there is one limper.

Preflop chart in SSHE says limp, in the notes section afterwards it says a raise can also be the correct play when folded to you or with one limper.

The middle pairs play best when multi-way or heads up, correct?

By raising EP you will get called by the hands that have you crushed (TT-AA) and also many of the so called coin flip hands (2 suited broadway, etc.). By limping you encourage multi way action, but often will get drawn out on by something that would have folded to a raise.

Raising allows you to "steal" the blinds every now and again, you will also often pick up a caller who will chase till the turn with overcards and fold...but you will also often get drawn out on and have to pay off the better hand.

Limping allows you to maybe see the flop cheap, and if you hit your set, you are well disguised and will probably win a big pot.

Always limping with these hands seems somewhat weak/tight to me. Always raising with them seems somewhat overaggressive to me. Can anyone shed some light on this for me. Thanks