Poolish advantages ?

Any preferment will give you a much deeper flavor profile. You would probably have a better texture as well from using a poolish.

A poolish is made at 100% hydration, mixed with a very small quantity of yeast (say, maybe a gram or two of your compressed yeast) and allowed to rise overnight. For this recipe you would want to use maybe 150 grams each of water and flour for the poolish. Then mix the final dough as normal, except with 150 grams less water and flour.

I believe most people don't use any less yeast in the final dough when using a poolish, but you might find you don't have to use as much. The rise may also go more quickly with the poolish.

"I would like some advice as what is/are the advantage(s) of using a poolish, rather than same day dough ?"

There are three key advantages; 

Flavor, flavor &  flavor.

Jeff

From what I've read in the sidebars in Jeffrey Hamelman's "Bread," poolish has the following effects:

- due to its protease activity, the finished dough will be more extensible (slacker)

-it will enhance the nutty aroma of the finished product

There's a formula in Maggie Glezer's Artisan baking (I believe the one for Acme baguettes) that suggests that poolish contributes flavor and aroma, while old dough contributes acidity, which enhances flavor as well as keeping quality. As for how to adapt the recipe, consult a tried-and-true formula using poolish in a favorite baking book, calculate the percent of total flour that is in the preferment, and apply that percentage to your formula.

I find using a poolish or other preferments to have all the advantages the other posters have mentioned. OTOH, I've also found that using a yeast preferment enables me to bake with the minimum amount of yeast.  I've recently baked a loaf weighing in around 900g with about two grams of active dry yeast that has been sitting in a freezer for almost two years. I believe I could have done the same with instant dry yeast. The standard packet or sachet of yeast, ADY or IDY, weighs 7g. You should try the same with your fresh yeast.

Most recipes use yeast as a method to speed up the process and end up losing much of the potential flavor. I find that time is the friend of flavor in a good loaf of bread. Just look at that poolish as a yeast farm, madly multiplying spores for your service in much the same way as a sourdough starter and creating flavoring compounds that are absent in heavily yeasted breads. If you step outside the box that recipes can put us in, you'll find better flavors and more understanding in how to bake a better loaf.

May I please add the fourth advantage to Jeff's advantage's list?

- More open crumb

 I find poolish based bread has more open texture with larger holes than straight dough and has lighter texture than using other forms of pre-ferment. Light but with deeper and complex flavour,  so it's  ideal pre-ferment especially for baguettes.

It may be....

..... due to its protease activity, the finished dough will be more extensible (slacker)

Poolish has been used to produce bread with more complex and improved flavour without having to ferment the whole dough  for a long time (takes up a large space).  Also Hamelman pointed out in his book that you can shorten the time for final proof by using poolish because fermentation process is enhanced by already active yeast in poolish.

Best,

lumos