More detailed warning message

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -501,9 +501,17 @@ ADIOS2IOHandlerImpl::flush(internal::ParsedFlushParams &flushParams)
 
 static constexpr char const *warningADIOS2NoGroupbasedEncoding = &R"(
 [Warning] Use of group-based encoding in ADIOS2 is discouraged as it can lead
-to drastic performance issues, especially when **not** used in conjunction with
-IO steps.
-We advise you to pick either file-based encoding or variable-based
+to drastic performance issues, no matter if I/O steps are used or not.
+
+* If not using I/O steps: A crash will corrupt all data since there is only
+  one atomic logical write operation upon closing the file.
+  Memory performance can be pathological depending on the setup.
+* If using I/O steps: Each step will add new variables and attributes instead
+  of reusing those from earlier steps. ADIOS2 is not optimized for this and
+  especially the BP5 engine will show a quadratic increase in metadata size
+  as the number of steps increase.
+We advise you to pick either file-based encoding or variable-based encoding
+(variable-based encoding is not yet feature-complete in the openPMD-api).
 iteration encoding for use with ADIOS2.
 For more details, refer to
 https://openpmd-api.readthedocs.io/en/latest/usage/concepts.html#iteration-and-series)"