Ok, so you have to consider what flavour it is that you're actually aiming for.....
We often think of a fruit flavour for an ingredient, but the flavour as it is when the fruit is in its natural form. Strawberry being an excellent example, as is Raspberry.
Now if it's in primary, then the fruit sugars will be fermented out and you end up with a completely different flavour to the one of the original fruit. Plus you have to manage the fermentation properly or you can get "capping" issues like with "proper" grape wine making. With the strawberry example, you often get little or no red colouration of the brew, it actually goes a pale straw colour and while it might smell of the strawberry aroma, most of the familiar taste is gone (some of it may recover a bit after ageing), raspberry can still smell great, but with the fruit sugars gone, you can get a very sharp, acidic taste from the fruit. Yes, depending on the colour and ripeness of the fruit, some pigmentation transfer, but not usually anywhere as deep as the original fruit.......
So then the other side of the coin, being that of putting fruit into secondary. You have to think of what the definition of "secondary" actually is. Is it when you're most of the way through primary ? or when primary is done and you've racked the batch off the gross lees ? And the actually "secondary" stage is more about clearing the batch ?
In any case, if you put fruit into secondary, you will most likely not ferment out all the fruit sugars, so the resulting flavour is more "fruit cordial" in character, or at least more fruity in the original taste, as was more likely considered/intended.
There are other issues to consider, like possible oxidation (especially with fruit involved), though most of those are negated by good practice.
Personally, I either do the secondary or I do both. If both, then I use 1/3rd of the fruit in primary, as that will help with pH buffering and nutrition, even though I have to make sure that the fruit stays moist as there's still the possibility of spoilage, yet the fruit in primary does seem to help with the final character of the brew, then once the ferment is complete, I carefully add the rest of the fruit. I use a gentle swirling of the fermenter to make sure that any floating fruit stays wet/moist and I always aim to let it drop before racking - I'm not always that patient, some fruit will show signs of good extraction of flavour/colour (strawbs and rasps tend to look paler/whiter etc). You usually get a much more fruit/cordial taste this way.
So as you can see, both techniques have pro's and con's, bring you back to what flavor it is that you're actually aiming for in the brew.......