So obviously if you cook it by poaching it, i.e. in boiling water, pitting it will cause some of the cooking water to enter the sausage and "steal" some of its taste, its smoke. So, okay, it's better not to prick it.
That said, cooking a sausage by poaching is not the best way to cook it, even if it is not pricked, the contact with boiling water is not necessarily interesting for the taste.
You will get a much better result with an oven cooking: Roll the sausage in a sheet of aluminium foil, put it on a plate or a dish and put it in the oven at 180° for about 40/45 minutes (in the case of a Morteau, 30 minutes for a Molène), the sausage will cook of course, but it will also caramelize a bit, and its taste will be sublimated by this long cooking at a reasonable temperature.
And by the way, spiked or not in this case? Well, a little bit as you want, if you prick some of the fat will escape and you will have a sausage a little less fatty, but also a little drier, it's up to you.
If you make a sausage in a bun for example, I strongly advise you to cook it in the oven.
In another case, the sausage is cooked in, or in contact with, its filling: potatoes, beans, lentils,..., then it's quite clear: you MUST prick, this way the taste of the sausage will fall (or go down) on the filling, the potatoes for example, and you will have an exceptional dish in taste!
I come back to the poached sausage, which is not pricked, in principle. I say "in principle" because in fact you can poach it if you want to do a double job, that is to say cook the sausage, but also obtain a very fragrant cooking broth from the water.
In this case, you will notice that the cooking water becomes cloudy and a little fatty as it cooks, because of the exchange that takes place with the sausage. At the end of the cooking process, remove the sausage, and you will have in the pan not only water but a "Molène broth" or "Morteau broth" that you can happily use to cook rice for example, vegetables, pasta, or a little bit of everything you want, and this cooking with broth will be much more tasty than a "l'anglaise" cooking (boiling salted water).
To sum up: Should a sausage be pricked before cooking? Well, it depends on the cooking method, and can we draw a general rule from this? Let's try it...
- Poached => do not poach, unless you want to obtain a broth at the same time
- Oven cooking => do not poach if you want to reduce the fat, but be careful => sausage is drier, otherwise do not poach
- Cooked in contact with the filling => we prick!
