Good question.
I have been speaking with the owner of a grow shop and he tells me that after a few weeks most of the nutrients are gone from new soil and that the good stuff from bat guano and worm castings run to the bottom and out the pot. I find that very hard to believe. In fact, I think it's not true and that he's selling ferts. How would our farmer's soils still be producing food for years if nutrients are used up in a month or two? But, for a small investment I can have organic fert that won't burn and I give moderate nutes to the plant. Yeah, it's probably not important the first month or so in new soil so I take it easy and dilute. I tend to doubt that new, quality soil is not enough for at least most of the vegitative time. If you use the right amounts and don't overfeed your plants you surely end up with better yields using nutes and I believe it only makes sense that during flowering you help your yield and potency by adding something.. But for a few months of vegging I would think new, excellent soil is plenty if that's all you want to use. Having said that, Peas Moss, Perlite, and 10% worm castings is a good growing medium but would not be a very nutrition rich soil at all on its own. If my soil was Peat, worm castings, mushroom compost, bat quano, mycorrhizae, and lime I would tend to believe that plants are going to have plenty of food during veg. Also, in my situation it's important to consider just how big I want my plants to be. I would be perfectly fine with a plant growing to 3 feet and budding in a 3 gallon pot because I don't need that much yield. But if I start a plant soon and prime it with ferts during the veg stage and it develops totally it's probably going to outgrow the pot and I have trouble later on... and if I have to transplant it to keep it healthy I run other risks of damaging or stunting it then too I believe.
I think the answer to your question lay in how good the soil you're starting with is. Also, some people would probably have some advice about adding some kind of nutrition that specifically helps a plant recover and thrive after transplanting.
By the way, it was explained to me that mycorrhizae forms its own nutrient rich root network within the soil that your plant's roots will plug into and suck nutrients out and that's why it's so valuable.. Is that more or less true?