Sure, it does seem to make sense: "My phone / laptop / iPad struggles to connect to the internet in here, so this is where I should place another wifi device."
It may even look good once you have set up a new access point. The wifi indicator on your phone or laptop may be showing a strong signal! After all, coverage from the new device is good!
However, it is highly unlikely that you have a fast and stable wifi network from here on out. Because all you have done, is move the coverage issue from the individual clients to the new access point.
And a wireless access point that itself is in poor coverage, cannot perform well.
First of all: We generally recommend against the use of wifi repeaters, and you can read more about why here: Five Reasons Not To Get A Wifi Repeater.
However, the same logic applies whether you already have one or more repeaters or you are setting up a recommended mesh network:
An access point must RECEIVE a strong signal to be able to PROVIDE a strong signal and perform reliably.
This is why you should not place the mesh node or repeater where coverage is bad. The new device should be placed at the outer edges of the area where coverage is good, either directly from the router or from another mesh node. A good rule of thumb is placing the new access point approximately half way between the previous access point and the area that has poor coverage.
This is the only way to actually extend good coverage.
An access point in poor coverage will never perform optimally and at worst, this can affect performance on the entire network.
You can read more about how this can happen here: Bad Apple: A Single Slow Device Can Bring Your Wifi Down.
How to place mesh nodes perfectly may vary somewhat with the manufacturer and mesh technology, but some rules of thumb apply generally.
Alle wireless access points benefit from being placed:
If you have big hindrances for wifi signals in your home, such as a steel armored bathroom or a central fireplace, triangulating your access point around this hindrance may be beneficial.
You can read more about which elements in a home are most problematic for wifi here: 10 Things In Your Home That Interfere With And Block Wifi Signals.
The next big question is of course: How do I know that the coverage is sufficient? Where do I check?
This may vary from product to product, but most wifi solutions these days have one or both of these:
At Eye Networks we like to recommend eero wifi, which we resell both to Nordic internet providers and to consumers in Norway.
When you install multiple eero devices in a mesh network, you will use eero's mobile app, and the app will simply prevent you from setting up a device when and if coverage is insufficient.