if you are referring to your own personal shopper score, that number is not displayed anywhere - instead, it is reflected in your Reputation badge level, and it's progress towards the next level. Simply put, you increase it's level by gaining shopper points, which is done by successfully completing shops (every shop done gives you a fixed amount of points), by completing courses on iSSprep, and by doing Opinion Polls on iSecretShop.
I hope this answers your question!
The shopper points system is quite simple - for each successfully completed shop, you gain shopper points. For each cancelled or declined shop, you lose points.
If your score is positive, it will not display as a score - you will be seeing your badges instead, as they are a more accurate and simple representation of your experience. If your score is negative, you will not be seeing the badges, but instead the exact sore (among other reasons, to help you keep track of how close you are to getting your score back to positive).
As soon as your score is positive again, you will be seeing all your badges (they haven't disappeared, they just won't be showing up while your score is negative).
I hope this provides some clarification.
It's up to individual companies to determine if they care about the badges. I pay little attention to them. However, the more shops you complete successfully, the more shops you can self-assign. I only shop a little bit on iSS - I primarily shop for companies not affiliated with this platform. However, I have done enough here to be able to self-assign five shops at a time (which is all I every really need/want here). There are folks who can do a lot more.
Badges can have various practical benefits, I'll list of them here:
These come to mind now, although there is probably more :) iSecretShop is always looking for ways to improve, and reward the active and reliable shoppers, so if you have any suggestions on what can be added to this, feel free to post :)