In general I would say no. That is too general of a question as it really depends on a lot of things.
If you have 1 SIP trunk and that's it, things are pretty simple. If you have multiple SIP trunks and providers, plus PSTN gateways, plus Bridges, then things are not as simple.
It really boils down to what YOU want to do and what your phone users are expecting. Do you want them to dial a -9- for an outside line. You can do that, but you don't have to. It can be an -8- or you don't have to make them dial a prefix at all.
For me I have two main SIP Trunks. One has cheaper rates but charges for calling toll-free numbers, the other one does not charge me for dialing toll-free numbers. So I have rules that route 800,888,877,etc. out that trunk but other calls out the other. I have a bridge so calls to certain extensions need to get routed that way.
Just remember, order matters (top-down). As soon as a call matches a rule it runs. So my 911 rules are first, then usually rules for the bridges, then my toll-free rules, then my other rules.
