Content created using field and content created using , and effect on website performance?
I'd recommend just using one field and changing the "Number of values" in the field settings. This will allow you to add as much as you want and yet only maintain one field.

In case you have different requirements, here's my opinion on the two approaches you are thinking of.

Here are the differences between the two approaches:

10 fields


you have many fields that each go through the preprocess, process, field_alter, and any other hook that might affect a field.
Assuming they are similar fields any maintenance you would do would have to be done on each on individually.
If the fields will eventually have different values then this approach allows you to easily modify them.


1 text area


you only have 1 field that does through the whole hook process. Which makes things go faster.
You only have 1 field to maintain.
It does not make sense to store multiple values in one textarea since it makes curating difficult and prone to typos. Imagine missing a closing div. Boom, layout gone.
Also, if in the future you have a case to migrate your content, you will have to make additional effort to migrate these since there are multiple values in the data.


All this said, the two options do not have a HUGE impact on performance if you're just loading them up for display and not doing massive preprocessing.