How good is BERT tokenizer?

I'm using [BERT pretrained](https://huggingface.co/tftransformers/bert-base-cased) for the 1st time & found smtg weird here. The original word 'demonstrators' has **split into 3 tokens that have different meanings**.

original = "Thousands of demonstrators"
tokenized= ["Thousands", "of", "demons", "##tra", "##tors"]

1. Will this affect the model performance?
2. What's the function of '##' here?

bert good languagetechnology