Output size grows rapidly with high repetition counts. Repeating a 100-character string 1000 times produces 100,000 characters, potentially crashing browsers or exceeding input limits. Monitor output size for large repetitions.
Separators must match output format requirements. Comma-separated values need ',', SQL inserts need ',\n', HTML lists need closing/opening tags between items. Wrong separators create invalid output requiring manual fixes.
Memory limits apply to very large outputs. Repeating text millions of times may exceed JavaScript string size limits (around 500 million characters in browsers) or available memory, causing errors.
Whitespace handling in separators needs attention. 'word' repeated with space separator creates 'word word word' with trailing space issues. Trim final separators or use join operations for clean output.