I don't agree with that, because that is exactly what I do. I have a hot wallet on my phone with usually less than $100 worth of bitcoin on it. I use this to make purchases in person with my local merchants who I know accept bitcoin. I'm buying things like groceries or electronic accessories such as spare cables, so usually well under $100. When it gets low, I top it up from a cold wallet at home.
If I plan to make a larger purchase than that in person, then I'll either load up my hot wallet in advance or take a hardware wallet and take it with me, depending on the value we are talking about.
You are very lucky to have some local merchants accepting Bitcoin. They accept payments with 0 confirmations or they are using LN? With a so low limit you are certainly rich and patient enough to top up your hot wallet several times a week but I don't think it's a veryconvenient limit for most people. If you need to receive or send funds to an exchange or a gambling site $100 won't be enough for example. Personally I don't think it's very safe to use his cold wallet for doing any transactions, but I understand people could do the opposite, especially if they don't use LN.