It may not be a big problem in terms of a currency collapse or something like that. I'm talking more so about Japan's anemic growth over the past few decades.
But there are some economic arguments suggesting that chasing growth for the sake of growth is a pointless exercise.
Ultimately, we have to ask which is of greater importance:
That some big, arbitrary number is slightly bigger than it was last year?
Or that the economy actually serves the purpose of supporting the people and businesses within that economy?
Output is directly related to wage levels, unemployment levels. Stagnant growth means falling wages, rising unemployment, etc. Not exactly an ideal situation for the population. Real wages in Japan are down 13% since 1997, if you can believe that. That's jaw dropping to me. https://en.wikipedia.org/wiki/Lost_Decade_(Japan)#Effects
I don't want to get into a philosophical discussion about Austrian vs. Keynesian economics here. That requires a much deeper dive. I'm just talking about the immediate economic effects of a "lost decade" scenario.