What's good about both exports and imports of a country rising at the same time? I recently came across a question that asks, if exports in a country rises by USD10 billion and imports rises by USD10 billion, what's good about both of these?

To my understanding, the GDP wouldn't change as Net Exports would be constant, so I'm not quite sure how exactly is this good or bad.
There are plenty of issues that can be relevant here, which mean it is hard to give a precise answer. On the one hand, even though GDP is not growing, at least the balance of trade is roughly unchanged. Some countries could experience an equivalent unaffected change in GDP via a trade deficit (e.g. if part of the fall in net imports is compensated with, say, an increase in consumption), which can fuel a currency depreciation and create inflationary pressures, not only on imported goods but on locally produced good which use imported inputs.

On the other hand, it is interesting to compare two countries with the same GDP but different level of exports and imports. The country with greater trade levels is more likely engaged in global value chains, which spur specialisation, and learning for local producers. The literature recognises the role of trade as a mechanism to spur technology transfer (and even transfer of ideas), thereby fostering productivity and growth.